Polymeric materials tend to fail or degrade due to mechanical fatigue, mechanical impact, oxidative aging due to radiation or impurities, thermal fatigue, chemical degradation, or a combination of these processes. The degradation can lead to embrittlement of the polymer, among other adverse effects. The embrittlement and associated cracking can advance to the point of product failure, which creates replacement costs. Mechanical fatigue and mechanical stress, such as that caused by dropping the object, can also lead to cracks that eventually cause failure. Thermoplastic and thermoset polymer systems used in products can be particularly susceptible to these failure modalities.
This problem is a great concern because of the widespread and intensive use in modern society of polymers in product components. For instance, polymers have a significant importance and presence in the electronics industry. Examples of applications include printed circuit board (PCB) laminates, housings, enclosures, adhesives, die attach, component packaging, and organic semi-conductors. In addition to the above-mentioned failure modes, other degradation processes, such as redox reactions or chemical diffusion, can be expected in organic semi-conductors and in electrically conductive polymers (which degrade their characteristics). Polymeric based paints are also subject to cracking due to environmental exposure causing degradation. Any polymer components used in the structure of equipment, such as airplanes or trains will be subject to long term degradation described above.
Traditional approaches to increasing the reliability of polymeric-based components and products have included a focus on suitable design enhancements and the use of incrementally improved plastics. Recently, a significant increase in the availability of so-called “smart” materials has occurred, which relates to materials that can sense impending failure and facilitate appropriate corrective measures to prevent extensive damage. Alternatively, if the damage has already occurred, some new material systems can purportedly self-heal the damaged structure. See, e.g., Chen, et al., “A Thermally Re-Mendable Cross-Linked Polymeric Material,” Science, Vol. 295, March 2002, pp. 1698-1702.
One recently developed process intended to impart self-healing capability to a polymer involves the incorporation of microcapsules containing a healing agent in a polymer matrix. White, S. R., et al., Nature, “Autonomic Healing of Polymer Composites,” 409, 794-797 (2001). The healing agent enclosed in the microcapsules is dicyclopentadiene (DCPD). A ruthenium polymerization agent, corresponding to CAS No. 172222-30-9, is dispersed in the polymer matrix. The healing agent is functionally active in the presence of moisture and air (oxygen source). When a fracture occurring in the polymer matrix propagates in close proximity of the microcapsules, the associated stresses caused by the fracture rupture the microcapsules. As a consequence, the healing agent is released from the ruptured microcapsules and contacts the fracture surfaces. The healing agent also comes into contact with a polymerization agent dispersed in the polymer matrix to the extent the dispersed polymerization agent is located in the direct vicinity of the fracture and released healing agent. When the polymerization agent contacts the self-healing agent, the healing agent is polymerized, resulting in filling of the crack planes of the fracture. This filling arrests fracture propagation and reduces the compliance of the post-fractured matrix material.
U.S. Pat. No. 6,518,330 B2 by S. R. White et al., describes a self healing polymer material, which relies upon rupture of microcapsules on contact with a fracture surface exposing a polymerizer to a catalyst. The reacting material within the crack fills the crack and adheres the crack faces together.
It is desirable, therefore, to provide a method for automatic repair of polymer failures that overcomes these and other disadvantages.